Modulators blowing

Gman1987

Why is this happening? i had 5 Mercury RF3000 bought off amazon. these take in video from our shed so to monitor cows calving. these modulators are connected in a loop thru before going to an amplifier/Distribution box. the problem is they keep blowing. i only have them about 1.5 years and i have gone through about 8 modulators. any ideas why this is happening? any solutions? any help would be greatly appriciated

Sam the Aerialman

Ger1987 wrote: »

Why is this happening? i had 5 Mercury RF3000 bought off amazon. these take in video from our shed so to monitor cows calving. these modulators are connected in a loop thru before going to an amplifier/Distribution box. the problem is they keep blowing. i only have them about 1.5 years and i have gone through about 8 modulators. any ideas why this is happening? any solutions? any help would be greatly appriciated

When you say it blows, Do you mean it shorts? How are the chain of modulators powered and are the cables stripped and bear and fed into one junction box? I'm going to hedge a guess that you're putting to much up power (It should only be 12V) through the chain and were it surges it blows.

The only solution i can think of is to use regulated 12V dc PSU's. You need to check the terminations and braiding to ensure they're not the cause of the short.

Gman1987

When i say it blows, i mean it just stops working, it is normally the last one in the series. please check out this link and it will show you how i have them connected up.
http://www.mccomp.plus.com/coolkit/ebay/pics/RF3000-surveillience.jpg
Each modulator is supplied with 9 volt power, these were supplied with the units when i bought them, these just plug straight into each modulator. Any ideas why its occuring? could it be that the signal feeds into a distribution/amplifier box and this box is sending current back up the aeriel cable and blowing the modulators? the distribution box is ran on 240 volts. Any help or solution greatly appricated

byte

Where are they sited?

Like, it'd be something I would expect if they are sited in a very cold/damp environment.

Gman1987

they are placed in tha attic in my house so no damp and we dont have attic insulation so heat from house will rise to the attic so its not cold either. Any other ideas? could it be possible that the Mercury modulators are just of very poor quality. I want to replace these modulators so dont want to have the same problem again

dowtchaboy

Is it a case of byre beware?:D

Sam the Aerialman

I think a simple bit of surge protection is required.

Its similar to daisy chaining extension leads, the voltage is being multiplied as it passes unit by unit and the end of the chain is the surge point. Check the dist amp if it has a 12V line power function that would be the beginning of the surge.

Antenna

Ger1987 wrote: »

could it be that the signal feeds into a distribution/amplifier box and this box is sending current back up the aeriel cable and blowing the modulators? the distribution box is ran on 240 volts. Any help or solution greatly appricated

Yes some distribution amplifiers can send DC current up to power a masthead amplifier - the user should be able to enable or disable this.
If for some reason you can't disable it, the simplest thing to do is pass the cable (between last modulator and amplifier) through an isolated TV socket - like this http://cpc.farnell.com/1/1/25227-single-flush-mounting-socket-apcoax7-isolated.html
(isolated will have capacitors visible on PCB at back)